A closed landfill in an old clay pit with ascending ground water was remediated by enclosure of the landfill body by a sealing wall and a surface sealing system
The landfill (LF) Hennickendorf has an area of 13.8 h. A volume of 2 Mio. m3 of waste was disposed between 1976 and 2001.
The LF is located in a former clay pit so a semi-impermeable barrier exists beneath, while a base liner system was not installed. The speciality of the site is the emergence of a high groundwater level. During operational phase a sump-drainage kept the water level constantly low, however, parts of the LF body was beneath water level.
After closure, the LF body was enclosed by a diaphragm wall in single-mass method. The sealing wall around the LF merged the semi-impermeable barrier, so lateral water flow from the adjacent groundwater body into the LF was stopped.
In a second step a surface sealing system was applied, with a geomembrane impeding water infiltration into the LF. The surface sealing system was completely structurally interconnected with the sealing wall.
In a third step groundwater management in the area around the LF was introduced and drainage facilities were installed to keep the overall groundwater level low.
After the encapsulation of the LF the only way water can enter the LF body is from beneath since water slowly penetrates the semi-impermeable barrier. The crucial point is that groundwater level within the LF body has to be kept below the outer groundwater level, so the groundwater flow direction always is into the LF body and pollutants do not leach into the outer zone. Therefore, sump drainage is temporarily necessary.
The financial resource needed for all described remediation measures was € 20,755,892.The measure was funded by ERDF with € 15,566,918 (75%).
Step 1: € 6,056,610
Step 2: € 13,315,252
Step 3: € 1,384,030
Evidence of success
The encapsulation of the landfill body by the sealing wall and a surface sealing system interrupt the contact of the landfill body with the groundwater and prevents the penetra-tion of rain water. The groundwater protection is guaranteed.
A impermeable layer beneath the LF is needed to guarantee the sealing wall effect. Contaminated water in the LF body has to be continuously discharged and treated to maintain the gradient between inner and outer groundwater zone.
Significant knowledge of construction of sealing walls is needed,
Potential for learning or transfer
On the territories of the EU member states exist about 500,000 landfills (LF). For the LF in the scope of the EU landfill directive only non-obligatory recommendations for remediation of all types of closed LF exist. For the more than 90% of the LF that predate the EU LF directive, no guideline or handbook on the remediation of these LF exist on European level.
This practice is applicable for cases where an effective protection of the environment from a LF caused groundwater-pollution is necessary, in particular, from those LF where the LF body is partly located within the groundwater table. Those landfills can only be LF that predate the EU LF directive because LF in the scope of the EU LF directive must have a proper geological barrier.
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